183 



Instances of irregular secondary thickening have been not in- 

 frequently cited. The classic examples of the plate roots in cer- 

 tain species of /■'ic/is, or notably in the roots of Parlda Africana, 

 may be mentioned, l)ut there the excessive thickening is practi- 

 cally wholly epinastic. l^pinastic or hyponastic thickening is 

 mentioned by llaberlandt as occurring in the main branches of 

 certain trees in the temperate region. Cases of diplonasty seem 



Fk;. I. Section of whole root showing V\g. 2. Enlarged view 01" transverse 



rings of annual thickening. The numer- section of the first thirty years of growth, 



als refer to the age. The twenty-fifth year The annual rings are represented alter- 



is marked by a slightly heavier line. The nately black and white. Magnified 



rind is black. Nearly natural size. about 3 diameters. 



to be rarer. Specific instances do not seem to be generally 

 cited in tlie ordinary literature ; at least the writer was unable to 

 find mention of any so well-marked case as that described above. 

 Such irregularities are no doubt more common than one is led to 

 believe from the references to them, and the writer would be glad 

 to see specimens of this kind. 



One naturally hesitates to make any too definite statement as 

 to the causes of such thickenings, but Ilabcrlandt's suggestion 



